Conventional A/D conversion techniques electrically achieve principal processing (sampling, quantization, and encoding) for converting analog signals into digital signals. Analog signals in the real world are processed using digital techniques in most cases. Thus, such A/D conversion techniques for converting analog signals into digital signals are essential in various fields. In particular, A/D conversion techniques are increasingly significant not only in the field of remote sensing (radar observation, astronomical observation, etc.) in which analog signals having extremely wide bands exceeding several tens of GHz but also in the field of information communication such as extremely wideband optical communication using 100 Gbps (Giga-bit per second). Thus, there is a demand for A/D converters which provide higher performances.
Today, there are electrical A/D converters that achieve a performance of approximately 100 Gsps (Giga-sample per second) at maximum, and each of these is configured by combining a plurality of A/D converters each providing a performance of approximately 10 Gsps. The performance of each of the electrical A/D converters depends on the performance of the 10-Gsps A/D converters which are base constituent elements. The A/D converters, however, have already reached a high degree of technical perfection, and it is difficult to achieve an ultra wideband exceeding the current ones due to problems of power consumption and time jitter during sampling.
In order to overcome these problems, converting A/D converters into optical A/D converters have been considered recently (see NPLs 1 and 2). NPLs 1 and 2 introduce a method for using non-linear optical effects such as self-frequency shifting or a method for parallel use of a plurality of optical active devices, as a method for converting the A/D converters into the optical A/D converters